String trimmers provide a versatile tool used in commercial and residential yard maintenance activities. These trimmers are particularly useful in trimming grass or edging along sidewalks, pavements, fences and similar borders.
When used to cut an edge, the cutting plane of the trimmer is rotated 90 degrees so that the cutting element rotates vertically. Since the cutting element rotates at a high speed, the guard which is positioned above and parallel to the cutting plane, is also oriented vertically. In this position, soil and vegetation cut by the string can be thrown outwardly and upwardly in a path extending radially from the cutting head.
To space the vertical cutting plane of the trimmer away from the operator in such situations, and thereby minimize the likelihood that they will be hit by flying debris, many trimmers have been provided with a curved support tube, so that when they are rotated 90 degrees, the cutting plane is spaced sideways from the operator.
To control the depth of the edge being cut, space the cutting element away from the operator and control the volume of the debris being thrown, trimmers have been provided with guides placed near the cutting head that roll or slide on the surface adjacent the edge being cut.
These guides also serve, when the trimmer is used to cut horizontally, to space it and its cutting element a given distance from walls, fences or similar objects. With this control over the spacing of the cutting plane from a given object, it is easier to achieve an even cut, prevent contact of the cutting element with the object and reduce cutting element wear.
Trimmer guides have often taken the form of rollers attached to the trimmer tube. These rollers include axles, bearings and miscellaneous support structures as well as members for attaching them to the trimmer. Being comprised of several parts, they can be costly to manufacture and assemble, incur rapid wear, require frequent maintenance and encounter failures as they are exposed to dirt, debris, water and similar contaminants.